Effects of selected silver nanoparticles on freshwater microbial communities

Due to their widespread use in consumer products an exposure of the aquatic environment to nanoparticles (NPs) is most likely. Especially metal/metaloxide NPs are widely used, of which silver nanoparticles (AgNPs) have gained considerable attention due to their broad microbiocidal properties implying a specific hazard for exposed aquatic algae and bacteria.In a case study with selected AgNPs (different sizes (10, 20 and 40 nm), and different coatings (citrate coated, non-coated)), the toxicity to natural freshwater microbial communities was determined. To distinguish between particle related effects and effects caused by free silver ions silver nitrate (AgNO3) was tested as a reference. The effects on the algal part of the community was studied through pigment profiling with HPLC. The bacterial community composition was analysed by metabolic profiling (ecologplates™). Inhibition of growth detected as a decrease in total biomass was seen in both bacterial and algal communities, for some cases in the range of environmentally realistic concentrations. Differences in toxicity could be determined for the different particles with AgNO3 being for almost all cases the most toxic compound with one excpetion. All experiments were backed up by analytical measurements (total silver content, dissolved silver (ultrafiltration), particle size distribution (Nanosight)).